Endoscopic surgical techniques are becoming increasingly popular in order to avoid exposing patients to unnecessary risks and extended recovery times which result from traditional surgical techniques. During endoscopic surgery, using normal insufflation procedures, carbon dioxide gas typically is used to distend the abdominal cavity, peritoneum, or other body cavity, so that the surgical instruments and telescope can be inserted therein.
Carbon dioxide gas is supplied from a compressed gas cylinder and is regulated down from the typical tank pressure of about 880 PSI or higher to about one-half PSI for distending the body cavity. Care must be taken to avoid overinflating the body cavity and risking possible harm to the patient.
Gas is delivered into the body cavity, such as an interabdominal cavity, during insufflation by a flexible tube having a hollow needle at the end thereof. The inlet end of the flexible tube is connected to the output port of the insufflator. The flexible tube and the body cavity of the patient form an enclosed pressure vessel or system. This enclosed system is inflated with the pressurized gas when the insufflation apparatus determines that the body cavity pressure is below a preset target level. The injection of the gas to increase the pressure can cause the patient cavity system to exhibit pressure variations and oscillations. Such variations and oscillations occur for a time period after the gas flow has stopped.
FIG. 1(a) is a pressure versus time diagram showing a typical pressure profile measured at the output port of the insufflator during insufflation. The pressure is maintained high at the output port of the insufflator while the gas is being delivered to the body. Because of this higher local pressure at the output port, accurate body cavity pressure measurements cannot be made while the gas is flowing into the body cavity. Furthermore, since the body cavity pressure is measured through the same line in which the gas is supplied, pressure measurements can be made only after the gas flow is stopped. After the gas flow is stopped, the gas in the body cavity moves away from the output port of the insufflator and continues to fill the cavity until the pressure in the cavity stabilizes.
When the gas flow is terminated, the pressure in the body cavity, delivery system, tubing, etc., begins to oscillate, as shown in FIG. 1(a). The body cavity pressure oscillates around the actual cavity pressure with steadily decreasing amplitude on the oscillations until the pressure in the system stabilizes at the body cavity-pressure. When the oscillations subside, accurate pressure readings can be taken.
However, it takes a substantial period of time before the pressure stabilizes ,enough so that accurate readings can be taken. If the pressure which is eventually measured is below the target inflation pressure, then additional gas must be introduced into the cavity, and the pressure measuring process must be repeated. The long waiting time required to allow the oscillations to subside is undesirable in that this increases the time required to complete the inflation. Also, during the surgical procedure, it is often necessary to continue to introduce gas into the body cavity, because of leakage and the like, in order to maintain the desired degree of inflation.
Thus, the waiting period while the pressure oscillations in the body cavity subside undesirably increases the time period of insufflation procedures. This increases surgical time and risk.